Typically, conventional ambient light sensors consist of a reversed biased photodiode, an amplifier, and an analog to digital converter (ADC). FIG. 1 is a schematic diagram illustrating a conventional ambient light sensor 100. Ambient light sensor 100 includes a reversed biased photodiode 102 for detecting light 104 that strikes ambient light sensor 100. Photodiode 102 is coupled to a voltage source 106 and a resistor 108. Resistor 106 is coupled to ground.
Ambient light sensor 100 also includes an amplifier 110 coupled to photodiode 102. Amplifier 110 amplifies the signal from photodiode 102. Ambient light sensor 100 also includes an analog to digital converter (ADC) 112 coupled to amplifier 108. ADC 112 converts the analog signal from amplifier into a digital signal for further processing. The spectral response of the photodiodes, such as photodiode 102, may be tuned, to the extent possible by the photodiode, to mimic the spectral response of the human eye.
Ambient light sensors, such as sensor 100, may be incorporated into electronic devices such as televisions, computer monitors, and cell phones. In these devices, ambient light sensors provide environmental illumination information to backlight controllers or front light controllers of displays in the electronic devices. The information provided by the ambient light sensors assists in determining the brightness of the display in these devices. For example, if the ambient light sensor detects that the environmental illumination conditions are bright (e.g. a cell phone outside on a sunny day), the brightness of the display may be increased so that images on the displays may be viewable in the bright environmental conditions.
These ambient light sensors, however, as designed to assume only homogeneous and static environmental illumination conditions. That is, these sensors assume that light from all angles is the same and the light does not change quickly over time. Because the ambient light sensors assume such illumination conditions, these sensors do not detect light well in settings where the intensity and direction of light may change rapidly, for example, within seconds or less. As such, these ambient light sensors are not suitable for devices such as avionics displays where lighting conditions may change rapidly. For example, fighter jets make rapid movements during flight, especially during combat. As such, the lighting conditions inside the cockpit of jet change rapidly as the jet maneuvers.
Additionally, these ambient light sensors are not designed to account for certain conditions of the human eye, such as behavior of the eye when exposed to flashes of light, the dependence of eye sensitivity to illumination history, the response of the eye to extremely patterned light, and the adaptation of the eye to contrast. As such, these ambient light sensors are not suitable where these conditions may be a factor.